The purpose of the project is to determine a suitable method for intravenous cholangiography in the presence of different degrees of common bile duct obstruction, and to use a new intravenous cholangiographic contrast agent. At present intravenous cholangiography is of very little value when the serum bilirubin is greater than 3mg%. Consequently more costly and dangerous diagnostic tests such as percutaneous transhepatic cholangiography and endoscopic retrograde cholangiography must be used. A safe, reliable, and inexpensive diagnostic test is desirable to determine preoperatively the etiologic and anatomic site of biliary tract obstruction, as well as distinguish obstructive jaundice from intrahepatic cholestasis. Recent clinical experiences, as well as investigations in our laboratory indicate that the new contrast agent, meglumine iodoxamate, produces denser ductal opacification than comparable doses of the only presently commercially available cholangiographic contrast agent, iodipamide (cholografin). Iodoxamate is expected to be approved for commercial use shortly. It will probably replace cholografin for routine intravenous cholangiography. The studies will be conducted on rhesus monkeys surgically prepared so that the common bile duct pressure can be raised to and maintained at any desired level. A series of different doses of iodine-125 labelled iodoxamate will be infused intravenously at various ductal pressures. Bile and blood will be collected, and the amount of radioactive iodine per sample determined with a well-scintillation counter. The amount of Iodine in the bile is directly proportional to its radio-opacity. The anatomic and metabolic effects of raising the common bile duct pressure will be evaluated by appropriate laboratory and radiographic studies.